The present invention relates to a suction duct as a passageway for supplying the air to an engine, and particularly relates to a suction duct in which noise at the time of sucking the air is lowered.
In a suction system of a motorcar engine, there is a defect that noise is generated in an air cleaner hose, a suction duct, or the like, when the air is sucked. This suction noise is harsh particularly at a low engine speed. Therefore, a side branch 201 and/or a resonator 202 is hitherto provided in a suction duct 200 as shown in FIG. 25, so as to reduce noise at a specific frequency calculated on the basis of Helmholtz resonance theory and so on.
The side branch 201 is, however, about 30 cm long if it is the longest, and the resonator 202 has a volume of 14 liters if it is the largest. Thus, the space in an engine room occupied by such noise absorption equipment increases and results in a defect that the degree of freedom to mount other parts is lowered.
Therefore, JP-U-64-22866 discloses a method in which an orifice is disposed in a suction duct, and suction noise is reduced by reducing the suction. By narrowing a suction passageway thus, acoustic mass increases so that suction noise in a low tone range can be reduced.
In addition, JP-U-3-43576 discloses a suction noise reduction apparatus which comprises two suction ducts connected in parallel to an air cleaner case, branch ducts branching from the two suction ducts respectively, and a common resonator to which all the branch ducts are coupled. The suction noise reduction apparatus further comprises an on-off valve which selectively opens in accordance with the driving condition and which is provided on the upstream side of a branch duct connecting portion in one of the suction ducts.
According to the apparatus disclosed in this publication JP-U-3-43576, the on-off valve is controlled in accordance with an engine speed so that the number of suction ducts is switched to one or two. Thus, the quantity of sucked air can be controlled in accordance with the engine speed, and suction noise can be reduced.
In the above-mentioned method in which the suction passageway is narrowed, however, there is a defect that the quantity of sucked air is insufficient at a high engine speed so that the output is lowered.
In addition, in the apparatus disclosed in this publication JP-U-3-43576, an electronic control circuit, an electromagnetic on-off valve, a diaphragm actuator, or the like, is used for driving the on-off valve. Those are not preferable in terms of the cost. In addition, since an electronic control circuit, an electromagnetic on-off valve, or the like, is necessary, the apparatus becomes not only complicated and expensive but also large in the number of man-hour for maintenance.
The present invention was developed in the light of such circumstances. It is an object of the present invention to provide a suction duct in which without narrowing a suction passageway and without using any electronic control circuit, any electromagnetic on-off valve, or the like, suction noise at a low engine speed can be lowered with a simple and low-priced configuration, and a sufficient quantity of the air can be supplied at a high engine speed.
A suction duct according to the present invention is characterized in that at least a part of a duct wall is formed out of a molded body of non-woven fabric in a suction duct disposed between an outside air intake of a motorcar and an intake manifold of an engine.
PET (polyethylene terephthalate) fibers, PP (polypropylene) fibers, PE (polyethylene) fibers, etc. can be used as fibers constituting this non-woven fabric. In view of fiber variation, quality, price, and so on, however, it is preferable that PET fibers are used.
In addition, it is preferable that the permeability per 1m2 of the molded body in the case of air with a pressure difference of 98 Pa is not larger than 6,000 m3/h in the above-mentioned suction duct. That is, xe2x80x9cpermeabilityxe2x80x9d herein means the quantity of the air passing through a test specimen in terms of unit area and unit time when the pressure difference between two chambers sectioned by the test specimen is set to be 98 Pa.
The above-mentioned suction duct is preferably configured so that the whole of the duct wall is formed out of the molded body, the non-woven fabric contains high-melting fibers of high-melting thermoplastic resin and low-melting fibers of low-melting themoplastic resin having a lower melting point than that of the high-melting fibers, and the ratio of the low-melting fibers to the non-woven fabric is higher than that of the high-melting fibers.
In the case where the suction duct is molded by compression molding, xe2x80x9clow-meltingxe2x80x9d herein means that a melting point is lower than the temperature in the compression molding, while xe2x80x9chigh-meltingxe2x80x9d means a melting point is higher than the temperature in the compression molding.
In addition, the suction duct may be configured so that the whole of the duct wall is formed out of the molded body, the non-woven fabric contains thermoplastic fibers constituted by a core material consisting of high-melting thermoplastic resin and a coating layer applied onto the surface of the core material and consisting of low-melting thermoplastic resin having a lower melting point than that of the core material, and the volume of the coating layer is larger than that of the core material.
The molded body of the above-mentioned suction duct may be formed out of non-woven fabric having a functional layer to which a predetermined function is given. Preferably, this functional layer is a water-repellent layer.
Further, according to the present invention, there is formed a suction duct which comprises a first segment having a substantially semicircular sectional shape and constituted by a molded body made of synthetic resin and a second segment having a substantially semicircular sectional shape and constituted by a molded body made of non-woven fabric, and in which the first and second segments are coupled integrally with each other.
The present inventors made researches earnestly on the relationship between the material of a suction duct and the noise generated therefrom. As a result, it was found out that, when a duct wall was formed out of permeable material having predetermined permeability, it was difficult to generate a standing wave so that suction noise was reduced conspicuously. The present invention was developed on the basis of such a discovery.
Noise generated at the time of air suction is chiefly caused by an acoustic standing wave generated inside a suction duct. The frequency of the standing wave depends on the length, diameter and material of the suction duct, and so on. Therefore, according to the present invention, at least a part of a duct wall of a suction duct is formed out of a molded body of non-woven fabric.
The reason why suction noise is reduced by forming a duct wall out of a non-woven fabric molded body is unknown in detail. However, the following three reasons are considered.
(i) Since non-woven fabric is an elastic body, it has a vibration damping effect, so that an acoustic wave is restrained from being generated by the vibration of the duct wall.
(ii) The energy of an acoustic wave entering a large number of gaps among fibers of the non-woven fabric is weakened by the effect of the viscosity and heat conduction of the gaps. In addition, the fibers themselves resonate with the fluctuation of the sound pressure so that the sound energy attenuates.
(iii) Since at least a part of the duct wall has a certain measure of permeability, an acoustic wave partially passes through the duct wall so that a standing wave is restrained from being generated.
It is considered that suction noise is reduced by the synergistic effect of these reasons.
However, when the permeability of the non-woven fabric molded body is too high, there is a defect that an acoustic wave inside the suction duct penetrates the duct wall and leaks to the outside so that noise increases. It is therefore preferable that the air permeability per 1 m2 to the air with a pressure difference of 98 Pa is not larger than 6,000 m3/h. The limitation that the air permeability is not larger than 6,000 m3/h per unit area is, of course, for the case of the air with a pressure difference of 98 Pa. It is a mater of course that the limitation value of the permeability is different if the suction pressure is different.
If the permeability per 1 m2 of the non-woven fabric molded body exceeds 6,000 m3/h, an acoustic wave passing through the duct wall of the suction duct increases so that penetrating noise increases. On the contrary, if the permeability is zero, noise is lower than in a background-art suction duct though the effect of restraining noise in a low frequency band of not higher than 200 Hz is lowered. To make the non-woven fabric molded body have zero permeability, it will go well if a surface skin layer like a film is formed on the external surface of the non-woven fabric molded body. Although the permeability can be made zero even if a surface skin layer is formed on the internal surface, this way is not preferable because it becomes difficult to reduce noise for the above-mentioned reason (ii). Incidentally, it is preferable that the permeability per 1 m2 of the non-woven fabric molded body to the air with a pressure difference of 98 Pa is larger than zero and smaller than 4,200 m3/h, and particularly larger than 0 and smaller than 3,000 m3/h.
At least a part of the suction duct according to the present invention has a molded body consisting of non-woven fabric. It is preferable that this non-woven fabric is formed out of thermoplastic fibers. If non-woven fabric made of thermoplastic resin fibers is used, even a suction duct having a complicated shape can be easily shaped and molded by hot press molding (heating compression molding) or the like. In this case, thermoplastic resin fibers may constitute a part of the non-woven fabric, or the whole of the non-woven fabric may be formed out of thermoplastic resin fibers. Alternatively, even non-woven fabric in which non-thermoplastic fibers are impregnated with a thermoplastic resin binder can be shaped by hot press molding or the like in the same manner as non-woven fabric formed out of thermoplastic resin fibers. Thus, suction noise can be reduced in the same manner as described above.
Indeed, the molded body consisting of non-woven fabric has a certain measure of effect on reduction in suction noise if the molded body exists in at least a part of the duct wall of the suction duct. But, a standing wave is generated easily with increase of a portion formed out of non-permeable material other than non-woven fabric. It is therefore preferable that the whole of the suction duct is formed out of a molded body of non-woven fabric.
However, in the case where the whole of the suction duct is formed out of a molded body of non-woven fabric, there is a case where a defect such as a crack or the like is generated in the wall surface so that suction noise leaks when the suction duct is to be formed to have a deep draw portion or a bent portion with a small curvature radius by hot press molding. In order to prevent such a defect, there can be considered a method in which the molded body is complicatedly divided into segments, and the segments are bonded into a predetermined shape. In this case, however, there is a defect that the number of man-hour increases so that the productivity deteriorates and the cost increases.
It is therefore preferable that the whole of the duct wall is formed out of a molded body, and the non-woven fabric is configured so as to contain high-melting fibers and low-melting fibers having a lower melting point than that of the high-melting fibers, while the ratio of the low-melting fibers to the non-woven fabric is higher than that of the high-melting fibers.
If the thus configured non-woven fabric is subjected to hot press molding, the low-melting fibers are softened and melted preferentially, while the high-melting fibers are deformed plastically or elastically. Finally, the softened low-melting fibers are cooled and solidified so that the non-woven fabric is formed into a predetermined shape. Thus, the degree of freedom for the fibers to move at the time of molding is so large that the non-woven fabric can be easily formed into a shape which has a deep draw portion or a bent portion with a small curvature radius. Even if a crack is generated on the wall surface, the crack is filled with the molten low-melting fibers existing plentifully so as to be welded and bonded. Thus, the above-mentioned defect is prevented.
It will go well so long as the volume of the low-melting fibers is larger than that of the high-melting fibers and it is preferable that the ratio of the low-melting fibers to the non-woven fabric is in a range of from 20% to 50%. If the ratio is smaller than 20%, the above-mentioned effect is difficult to appear. On the contrary, if the ratio is larger than 50%, the molded body is insufficient in heat resistance. Incidentally, it is preferable that the melting point of the low-melting fibers is in a range of from 150xc2x0 C. to 170xc2x0 C. and the melting point of the high-melting fibers is in a range of from 220xc2x0 C. to 260xc2x0C.
The non-woven fabric may contain other fibers than the high-melting fibers and the low-melting fibers. Although such other fibers are not limited specifically, it is also preferable that fibers having a special function, such as water-repellent fibers or the like, is used.
Further, it is also preferable that the non-woven fabric is configured to contain thermoplastic fibers constituted by a core material consisting of high-melting thermoplastic resin and a coating layer applied onto the surface of the core material and consisting of low-melting thermoplastic resin having a lower melting point than that of the core material, and the volume of the coating layer is larger than that of the core material.
With the non-woven fabric configured thus, the coating layer is softened and melted preferentially at the time of hot press molding, while the core material is deformed plastically or elastically. Finally, the softened coating layer is cooled and solidified so that the non-woven fabric is formed into a predetermined shape. Thus, the degree of freedom for the fibers to move at the time of molding is so large that the non-woven fabric can be easily formed into a shape which has a deep draw portion or a bent portion with a small curvature radius. Even if a crack is generated on the wall surface, the crack is filled with the molten coating layer existing plentifully so as to be welded and bonded. Thus, the above-mentioned defect is prevented.
It will go well so long as the volume of the coating layer is larger than the volume of the core material, and it is preferable that the ratio of the thermoplastic fibers to the non-woven fabric is in a range of from 20% to 50%. If the ratio is smaller than 20%, the above-mentioned effect is difficult to appear. On the contrary, if the ratio is larger than 50%, the molded body is insufficient in heat resistance. Incidentally, it is preferable that the melting point of the coating layer is in a range of from 150xc2x0 C. to 170xc2x0 C. and the melting point of the core material is in a range of from 220xc2x0 C. to 260xc2x0 C.
In the case where non-woven fabric partially containing thermoplastic fibers with such a double-layer structure is used, it is preferable to use non-woven fabric containing at least 20 to 50 volume % of such thermoplastic fibers. If the content of the thermoplastic fibers is smaller than 20 volume %, the above-mentioned effect is not exhibited well so that a crack may remain in the molded body.
In the suction duct according to the present invention, the thickness or characteristic of the molded body may change due to aged deterioration, moisture penetration, or the like. As a result, the balance between penetrating noise passed through the molded body and suction noise radiated from a suction inlet at a front end of the suction duct may be lost so that the performance of restraining the suction noise may change.
It is therefore preferable that the molded body is formed out of non-woven fabric having a functional layer to which a predetermined function is given. A water-repellent layer, a clogging preventing layer, etc. are exemplified as such a functional layer. Such a molded body can be formed easily by using non-woven. fabric in which fibers having their own functions are mixed in their suitable portions. Alternatively, films having their own functions may be laminated on non-woven fabric in use.
The above-mentioned xe2x80x9cclogging preventing layerxe2x80x9d herein means a film like cover which covers the external surface of the suction duct consisting of non-woven fabric so that a free space having an enough size not to prevent the airs in the suction duct from passing through the duct wall consisting of the non-woven fabric is provided between the external surface of the suction duct and the cover (see FIGS. 26A and 26B). The cover is fixed to the external surface of the suction duct by a tape or the like.
The position of this function layer can be set desirably in the thickness direction of the molded body. For example, in the case where a water-repellent layer is used, it is preferable that the water-repellent layer is provided on a surface layer or an intermediate layer of the molded body. Thus, moisture is prevented from invading the molded body. As a result, the characteristic of the molded body is prevented from changing so that the effect of reducing suction noise can be kept for a long time. In addition, water is restrained from invading an air cleaner so that it is possible to restrain engine trouble caused by the loss of the permeability of air. cleaner elements.
Incidentally, in the case where a cylindrical body such as a suction duct is manufactured by compression molding, it is usual that a plurality of segments, such as first and second segments each having a substantially semicircular sectional shape, are formed by compression molding, and then the segments are bonded integrally with each other. In addition, in order to increase the bonding strength of the segments, generally, flange portions are formed in each segment on its opposite sides, and those flange portions of the segments are bonded with each other so that the bonding area increases. Also in the case where the suction duct is formed out of non-woven fabric, it is preferable that a similar method is adopted, and the flange portions on opposite sides of the segments are bonded integrally with each other.
However, in the suction duct manufactured in such a method, the portion where the flange portions are bonded with each other becomes about twice as thick as any other ordinary portion, so that the rigidity increases. As a result, it is considered that it is difficult to absorb vibration when the suction duct is in use so that there arises a defect in durability or in vibration noise.
In addition, any portion other than the flange portions is insufficient in rigidity so that the shape retentivity is low. As a result, there is a defect that such a portion buckles up when large negative pressure or external force acts thereon, or the positioning accuracy is low when the suction duct is. attached to a partner member.
Taking such circumstances into consideration, it is preferable to manufacture a suction duct which has a hard portion with high compressibility and a soft portion with low compressibility, and which is formed out of non-woven fabric containing a thermoplastic resin binder by compression molding.
Moreover, in the above-mentioned suction duct, it is preferable that the hard portion extends linearly.
Further, in the above-mentioned suction duct, an engagement portion which can engage with a partner member may be formed in the hard portion.
Then, in the suction duct according to the present invention, a plurality of segments are formed out of non-woven fabric containing a thermoplastic resin binder by compression molding so that each of the segments has a substantially semicircular sectional shape with flange portions on its opposite sides respectively. The flange portions of the segments are bonded with each other so that the segments are formed into a cylinder, and a deformable flexible portion is provided in at least a part of the flange portions.
The non-woven fabric used for the above-mentioned suction duct contains a thermoplastic resin binder. That is, it is possible to use non-woven fabric in which non-thermoplastic fibers are impregnated with a thermoplastic resin binder, non-woven fabric which contains thermoplastic resin fibers as a binder, or the like of them, the non-woven fabric which contains thermoplastic resin fibers is used preferably. If the non-woven fabric which contains thermoplastic resin fibers is used, even the suction duct having a complicated shape can be shaped and molded easily. In this case, the thermoplastic resin fibers may constitute a part of the non-woven fabric, or the whole of the non-woven fabric may be formed out of the thermoplastic resin fibers. In the case where the whole of the suction duct is formed out of a molded body of non-woven fabric, it is preferable that the flange portions on the opposite sides of the segments are bonded integrally with each other. However, the portion where the flange portions are bonded with each other about twice as thick as any other ordinary portion, so that the rigidity increases. As a result, there arises a defect as mentioned above.
Therefore, the suction duct according to the present invention has a hard portion with high compressibility and a soft portion with low compressibility. With such a configuration, the soft portion is rich in flexibility enough to be deformed easily and to follow external force easily. It is therefore possible for the soft portion to absorb vibration when the suction duct is in use, so that the durability is improved and noise due to vibration can be restrained from being generated. In addition, various properties can be given to the suction duct by selecting the positions or sizes of the soft and hard portions.
Incidentally, there is no specific limitation so long as there is a slight difference in compressibility between the soft portion and the hard portion. The difference in compressibility may be set desirably in accordance with applications, use conditions, and so on.
It is also preferable that the hard portion is configured to extend linearly. Thus, the hard portion acts like a reinforcing rib, so that the shape retentivity is enhanced. For example, if the hard portion is formed in the circumferential direction of the suction duct, the suction duct is prevented from buckling even if excessive negative pressure or external force acts on the suction duct. Further, if the hard portion is formed in the direction in which the suction duct extends, the shape retentivity is enhanced so that the accuracy in attaching the suction duct to a partner member is enhanced.
It is also preferable that the hard portion is formed to have an engagement portion which can engage with a partner member. As the engagement portion, engagement claws, attachment flanges, etc. are exemplified. If such an engagement portion is thus formed in the hard portion, other parts become unnecessary. As a result, the number of parts is reduced so that the number of man-hour can be reduced, and the cost can be reduced. In addition, separation in recycling becomes so easy that the recyclability is enhanced. Incidentally, since the engagement portion is formed in the hard portion with high compressibility, the strength of the engagement portion can be ensured sufficiently. It is also preferable that only the compressibility of the engagement portion is made further higher.
Further, it is also preferable that at least a part of the flange portion is provided with a deformable flexible portion. When vibration occurs, the flexible portion is deformed to absorb the vibration, so that the durability is enhanced while noise due to the vibration can be restrained.
As the shape of this flexible portion, a corrugated shape in which mountain portions and valley portions are alternated continuously is representatively exemplified. Incidentally, it is also preferable that a flexible portion is provided not only in the flange portion but also in a cylindrical ordinary portion. As a result, the suction duct is deformed more easily so that the vibration damping property is further enhanced.
Further, the suction duct may be constituted by first and second segments each having a substantially semicircular sectional shape, one of the segments being formed out of a resin molded body, the other being formed out of a non-woven fabric molded body. Since the first segment formed out of a resin molded body has large rigidity, so that a bracket portion or a fitting portion for fixing the suction duct to an air cleaner can be formed integrally with the first segment. Thus, the number of parts is reduced so that the productivity is enhanced. In addition, the assembling property and reliability are also improved.
The first and second segments may be coupled integrally with each other through a clip or the like prepared separately. In this case, however, there is a defect that the number of parts increases. It is therefore preferable that the first and second segments are coupled by themselves. For example, there is a method in which the first and second segments are coupled mechanically through an engagement means such as engagement claws formed in the first segment; a method in which the first and second segments are coupled by welding; and so on. The first segment has enough strength because it is made of resin, so that the engagement means such as engagement claws can be formed integrally with the first segment.